212 
Aqua  Pur  a. 
Am.  Jour.  Pnarm. 
April,  1897. 
ingredients  be  not  stirred  during  effervescence,  there  is  a  danger 
that  the  contents  may  be  thrown  from  the  container. 
The  reaction  between  the  fat  and  acid  is  sometimes  slow  in  re- 
sponding, and  when  it  responds  it  does  so  very  quickly.  For  this 
reason  the  writer  prefers  to  withdraw  the  heat  on  active  effervescence, 
and  then  after  the  reaction  is  in  operation,  to  heat  gently  until  effer- 
vescence ceases,  rather  than  to  follow  the  official  directions  of  heat- 
ing until  effervescence  ceases  after  the  addition  of  acid  with 
primary  reaction. 
There  is  no  apparent  need  of  waiting  until  the  temperature  of  the 
oxidized  fat  falls  to  400  C.  (1040  F.)  before  adding  the  mercurial  so- 
lution. Squire  cools  his  product  to  6o°  C.  (1400  F.),  and  this  would 
seem  to  be  a  low  enough  temperature. 
The  red  oxide  of  mercury  "  lumps  "  slightly  on  adding  it  to  the 
acid,  but  heat  soon  brings  it  into  solution. 
Objection  may  be  made  to  the  addition  of  glycerin  to  ointment  of 
mercuric  nitrate,  on  the  ground  that  nitro-glycerin  may  be  formed. 
The  objection  is  not  well  founded.  The  production  of  nitro-glycerin 
requires  a  large  excess  of  concentrated  sulphuric  acid  over  the 
quantity  of  nitric  acid  used  in  order  probably  to  absorb  rapidly  the 
water  formed  in  the  reaction,  as  follows : 
QH5  (OH),  +  3N02'OH  =  C3H6  (N03)3  +  3H20 
This  condition  does  not  obtain  in  this  ointment.  In  addition, 
the  fat  present  doubtless  inhibits  such  a  change.  Further,  the 
writer  has  followed  the  practice  of  adding  glycerin  to  the  ointment 
for  three  years  past,  and  there  has  been  no  complaint  of  untoward 
therapeutic  effects,  as  there  would  have  been  had  any  nitro-glycerin 
been  present ;  the  latter  is  rapidly  absorbed  by  the  skin. 
AQUA  PURA. 
Editor  American  Journal  of  Pharmacy. 
Dear  Sir  : — In  consideration  of  the  condition  of  the  drinking 
water  supplied  to  the  citizens  of  Philadelphia  and  some  other  cities, 
too,  by  their  public  works,  it  seems  to  me  there  is  an  excellent 
opportunity  for  the  pharmacist  to  do  a  stroke  of  business  as  well  as 
to  assist  his  suffering  fellow-beings  to  preserve  their  lives  and  en- 
joy a  drink  of  pure  water  while  still  living.    My  suggestion  is  that 
